Field of Invention
The invention relates to a device or supplying a fuel cell battery and to a method for supplying a fuel cell battery.
Background Information
Fuel cells and thus also fuel cell batteries are elements of fuel cell systems and allow a utilization of energy of a fuel by energy conversion. In this respect, both electric energy, which is generated on the basis of electrochemical processes, and thermal energy, which arises in the form of hot waste gases, can be utilized. Gaseous flows of two reactants are conducted separately through the cells for this purpose. The first reactant, which is in particular environmental air, contains oxidizing components; the second reactant contains reducing components. A gas which in particular contains methane (e.g. natural gas) is used as the second reactant which is conducted through a reformer prior to the entry into the cells and which is there converted into the reducing components of hydrogen and carbon monoxide.
The reactants are fed into the fuel cell battery in a quantity ratio which is characterized by the so-called air number (or air ratio) λ related to the stoichiometry. So that no reducing components, that is non-combusted components, of the second reactant are no longer contained in the exhaust gas flow, it must be ensured that the air number λ is always larger than or equal to 1. It is thus ensured that there is always sufficient oxygen present for the complete oxidation of the hydrogen and of the carbon monoxide and thus a reliable operation of the fuel cell battery is ensured.
It must in particular be ensured that, with an insufficient first reactant flow, that is in particular with an insufficient environmental air flow, the second reactant, that is in particular natural gas, is not still supplied to the fuel cell battery. If natural gas were also still to be supplied in this case, it could have the result that non-combusted hydrogen and non-combusted carbon monoxide leaves the fuel cell battery and combusts in an uncontrolled manner outside the fuel cell battery.
It is known that the first reactant flow is monitored by a monitoring element which can generate an error signal in dependence on a parameter of the first reactant flow, said error signal indicating an insufficient first reactant flow. The monitoring element can, for example, be designed as a pressure switch which is arranged in parallel with a pressure drop generation element, for example in the form of a diaphragm. The pressure switch generates an error signal when a pressure drop at the pressure drop generation element is smaller than a threshold value. This is the case when the throughflow of the first reactant through the pressure drop generation element is too small. This error signal is received by an automatic firing device which, in response to said error signal, controls a shut-off element which interrupts the second reactant flow, that is in particular a natural gas flow.
So that the described interruption works reliably on the presence of an insufficient first reactant flow, the monitoring element must naturally also operate without error, that is always generate the error signal whenever necessary. It is a legal requirement in at least some countries that the operational reliability of the monitoring element is checked regularly, for example at least once every 24 hours. With known systems, for this purpose the supply of the fuel cell battery is deliberately interrupted at regular intervals, for example every 24 hours, and the fuel cell battery is thus shut down. As soon as the supply of the fuel cell battery with the two reactants is interrupted, a functional monitoring element generates the named error signal. If this is the case, the fuel cell battery can be started up again. If no error signal is generated, there is a defect in the monitoring element and the fuel cell battery may not be started up again without a previous further check.
The shutting down and subsequent starting up of a fuel cell battery interrupts the electric power generation of the fuel cell system, requires energy and additionally has negative effects on the service life of the fuel cell battery.